VirtualBox supports multiple monitors for guest virtual machines (VMs). Display for guest VMs can be either attached to multiple windows on host machine as "virtual" monitors, or hooked up with multiple physical monitors.

In this tutorial, I will describe how to set up dual monitors for Ubuntu Guest on VirtualBox, so that the display of Ubuntu Guest VM will appear in two separate windows on host machine, as virtual dual monitors. This tutorial has been tested on Ubuntu Desktop 12.10 and 13.04, and VirtualBox 4.2.12.

First, power off Ubuntu Guest VM, if it's running.

Then, open up "Display" setting of Ubuntu guest VM on VirtualBox. Under "Video" tab, increase monitor count from 1 to 2.

Now power on Ubuntu guest VM.

In order to use multiple monitors on a guest VM, you need to install Guest Additions inside the VM. To install Guest Additions on Ubuntu guest VM, run the following.

For Ubuntu 12.10 or before:

$ sudo apt-get install virtualbox-ose-guest-x11

For Ubuntu 13.04 and higher:

$ sudo apt-get install virtualbox-guest-x11

After installing Guest Additions, power off the guest VM, and restart it.

Upon boot, go to System Settings -> Displays on Ubuntu Desktop to configure dual monitors.

Uncheck "Mirror display" box, in order to double the desktop space of guest VM across two displays. You should also see two monitor icons (labeled "VBX 0") side by side as shown below. Drag the monitor icons around to re-arrange the relative position of the two monitors (e.g., vertically or horizontally). If you want, click on a specific monitor icon in order to adjust the resolution of the corresponding display, or turn it on/off.

The following screenshot shows the virtual dual monitors for Ubuntu Guest in action.

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Dan Nanni is the founder and also a regular contributor of Xmodulo.com. He is a Linux/FOSS enthusiast who loves to get his hands dirty with his Linux box. He likes to procrastinate when he is supposed to be busy and productive. When he is otherwise free, he likes to watch movies and shop for the coolest gadgets.